The present invention relates to a measurement procedure and a flowmeter as defined in the claims.
Especially when searching for suitable places for final placement of nuclear waste, it is necessary to obtain information as to what sort of currents are occurring in the rock and its crevasses, i.e. what are the directions and velocities of flow of the currents.
In such measurements, the small volume flows and low flow rates cause problems. In prior art, a method used for determining the magnitude of flow is to separate a certain portion of a hole cut in the rock and to fill it with a suitable mixture or solution. By monitoring the changes in the concentration of this mixture or solution, it is possible to measure the flow. However, this method provides no information about the direction of the flow.
Attempts to determine the flow directions include the use of various marking substances whose passage in the chinks in the rock can be monitored.
A problem with all known methods for flow measurement is that they are slow. Since the rates of flow are of the order of a milliliter per hour, performing a single measurement generally takes months and thus getting results from a large area and multiple bore holes is an expensive and slow business.